1. Field of the Invention
The present invention relates to a vehicle driving system with an electric motor, and typically to a technique for improving controllability of an electric motor.
2. Description of the Related Art
Known techniques relating to a vehicle driving system with an electric motor include those relating to a vehicle driving system mounted in a four-wheel drive vehicle which uses an engine to drive one of two pairs of wheels (i.e., either front or rear wheels) and uses an electric motor to drive the other pair of wheels. These conventional techniques typically employ a speed sensor to detect a rotating speed of the electric motor (refer to JP-A-2005-253196 and JP-A-2006-87185). In addition, a common way of detecting this rotating speed using a speed sensor is by calculating a pulse period from detected edges of pulses and deriving the rotating speed.